Soil Roughness Effects on Runoff and Sediment Production

The effect of soil surface roughness on runoff and sediment production is an area not yet fully quantified. Current erosion prediction models, such as the Revised Universal Soil Loss Equation, predicts a reduced erosion from an increased soil roughness, without considering the functionality associated with different roughness forms. In this research, we used a mechanistic approach in which soil roughness is partitioned into depressions and mounds and their effects on runoff and sediment production are quantified separately. A laboratory rainfall simulation experiment was conducted using paired rough versus flat surfaces in a 5 m soil box. Depressions delayed the runoff initiation by storing water into puddles and enhancing infiltration. Surface mounds did not delay runoff initiation. Once runoff reached a steady state, rough surfaces either with depressions or mounds produced mostly greater runoff with either an increased or decreased sediment flux, despite a high degree of data scatter. This effect persisted until the roughness elements disappeared, suggesting the flow concentration on rough surfaces was a likely cause. Surface roughness, subsurface condition (ie. seepage or drainage), flow erosivity and rainfall intensity and duration all affected the soil losses. Our results show no simple relationship between roughness, flow and erosion exists and the net effect on runoff and erosion depends on the dominant form and its functionality. Additional